Canine hip dysplasia (CHD) is a common problem in veterinary medicine. CHD is a coxofemoral joint deformity which is not apparent at birth but develops during puppyhood, frequently resulting in severe arthritic pain and immobility. CHD occurs among many breeds of dogs, but has a higher incidence and severity among larger dog breeds having an average adult body weight of 35 pounds or more. Generally, the larger the size of a breed, the higher the incidence of CHD.
The principal clinical symptom of CHD is subluxation of the hip joint, an indicator of hip joint laxity, which causes abnormal wear and degeneration of hip joint tissue. Laxity of the hip joint begins a cycle in which movement by the animal forces the femoral head into an abnormal position in the joint. The abnormal positioning of the femoral head causes erosion of the joint cartilage and inflammation of the synovial membrane surrounding the joint. The end result of chronic joint laxity is an abnormally shallow acetabulum and a flattened femoral head, resulting in joint pain, instability and immobility. A similar mechanism is involved in the development of osteoarthritis. Research has shown that reduction of hip joint laxity during early growth helps to prevent the development of CHD and osteoarthritis in dogs.
Research also suggests a correlation between accelerated bone growth during the first nine months of puppyhood, and the development of CHD. The first nine months of life are considered to be a critical period for hip joint development in the dog. During this period the acetabulum is growing at an accelerated rate relative to the femoral head. The accelerated growth rate renders the acetabulum more plastic and particularly susceptible to malformation under the influence of hip joint laxity. It ha; been postulated that reduction of overall bone growth rate during the first nine months of life can improve hip joint congruity by reducing the disparate growth rate between the acetabulum and the femoral head.
Typically, diagnosis of CHD is accomplished by standard radiographic methods, which are approximately 70% accurate overall, with increasing accuracy of diagnosis the closer the animal is to 2 years of age. Radiographic diagnosis relies on a finding of subluxation of the feinoral head. The severity of CHD as deduced from clinical presentation does not always correlate well with actual radiographic measurements because of the confounding influence of individual and breed variations in temperament and body structure.
CHD has a genetic basis, with heritability most frequently estimated to be about 0.30. For example, a heritability of about 0.3 indicates that about 30% of the variation in occurrence of CHD is attributed to parentage, while the remaining 70% is attributable to environmental factors or interactions with environmental factors. The exact nature of the environmental factors which affect CHD incidence and severity is not known for certain, and clinically the disease is highly variable among individual dogs. However, evidence supports the contention that diet and feeding are significant factors affecting hip joint laxity and the development of CHD, and suggests that manipulation of diet, especially during the early stages of bone development, might be one way to treat CHD. Dietary methods for treating CHD are especially attractive because typically they are easily practiced.
A known dog food composition and feeding method exists for reducing hip joint instability in dogs. The composition has a specified dietary anion gap (DAG) of no more than about 20 milliequivalents/100 g of food. Dietary anion gap is calculated as: Na (mEq/100 g)+K (mEq/100 g)-Cl (mEq/100 g). The feeding method relies on administration of the composition during the early years of growth, and reduces subluxation of the femoral head. Another known feeding method, limit feeding, improves hip joint stability and reduces the incidence and severity of CHD by reducing the overall growth rate and bone maturation rate of pups. However, the known dog food compositions and feeding methods provide incremental amelioration of subluxation, and a need remains for dog food compositions and feeding methods which further reduce hip joint laxity and the severity of CHD.
It would be desirable to provide a method of reducing the incidence and severity of CHD and osteoarthritis by reducing hip joint laxity in dogs. It would also be desirable to provide such a method which is dietary in nature and easily practiced. It would be further desirable to provide a nutritionally balanced dog food composition which substantially improves hip joint congruity and ameliorates CHD and osteoarthritis. It would be still further desirable to provide such a dog food composition which, when fed to puppies during the early years of growth, reduces hip joint laxity and thus the severity of CHD in mature dogs.